Update services.xml

This updates the service used for the first constructor argument in services which use the CmfBlockHelper.

Catchable Fatal Error: Argument 1 passed to Symfony\Cmf\Bundle\BlockBundle\Templating\Helper\CmfBlockHelper::__construct() must be an instance of Sonata\BlockBundle\Templating\Helper\BlockHelper, instance of Sonata\BlockBundle\Twig\Extension\BlockExtension given, called in app/cache/test/appTestDebugProjectContainer.php on line 1199 and defined in vendor/symfony-cmf/block-bundle/Symfony/Cmf/Bundle/BlockBundle/Templating/Helper/CmfBlockHelper.php line 32

ping @dbu